Optical characterization of hydrogenated amorphous carbon (a-C : H) thin films deposited from methane plasma

Hydrogenated amorphous carbon (a-C:H) thin films are deposited at low-press ure (0.35 Pa) on c-Si substrates from methane plasmas. The plasma enhanced chemical vapor deposition (PECVD) process is operated in a dual electron cy clotron resonance (ECR)- radio frequency (r.f.) reactor using an independen tly controlled r.f. substrate bias. The film,growth and substrate temperatu re are monitored in situ using real time kinetic ellipsometry and fluoropto metry. The deposited films are investigated by means of ex situ UV-Visible (1.5-5.0 eV) spectroscopic ellipsometry and Fourier transform infrared spec troscopy (500-4000 cm(-1)). The dielectric functions are determined from th e ellipsometric spectra using Jellison and Modine's dispersion model wherea s the structure of the films is examined through the use of absorption spec tra. Complementary Raman measurements performed at 457 nm reveal the presen ce of the two main graphitic G and D peaks as well as two additional bands located at about 1170 and 1470 cm(-1). It is shown that a-C:H film optical properties change from polymer-like to diamond-like depending on the energy and flux of the hydrocarbon species impinging on the substrate. (C) 2000 E lsevier Science S.A. All rights reserved.